MDF - Smooth edge

Joined
6 Jul 2007
Messages
217
Reaction score
0
Location
London
Country
United Kingdom
Hi

I am making a "star" mirror out of mdf.

It has a lot of pointed/triangular bits coming out of a round "centre" frame. The "arms" of the star have V-grooves routed into them and some are chamfered too.

Because of this, there are a lot of sawn/routed edges which, being mdf are quite rough. I would like them to be as smooth as possible. I have read many previous posts on smooth edges with mdf and it seems that the two main bits of advice are to use wood filler or plaster (which can crack).

I was wondering whether there was any other thing that I could do. I would like a nice smooth finish but at the same time, it doesnt need to be like glass. I have tried the wood filler but with so many grooves and edges it is both time consuming and very difficult to apply without spoiling the routed bits.

Any advice much appreciated!!!

Thanks :D
 
Sponsored Links
is it going to be painnted, if so then don't worry about it give it acoat of primer let this dry completely any of the bristly bit will be stuck up give it a light sand and repaeat a couple of times until you have a smooth surface you may need to denib it again after the undercoat but it should be pretty smooth
 
Hi CHappers

Thanks for your reply.

It is going to be painted. I had hoped to find an aerosol spray primer (Zinsser BIN) and aerosol silver paint once primed to avoid brush marks and/or small bubbles from foam rollers.

I have read that using the BIN primer with a little sanding in between the 2-3 coats gives a glass like smoothness. Is this true? Also, what grit sandpaper should i go through and should i do it by hand or, where possible, should/can i use a palm sander (little Makita one)?

Thanks again! :)
 
unsure mate never used it, give it a go and see how it comes up , you can always sand it back and go down a more conventional route finishing off with a feww coats of spary top coat to get your desired finish.
 
Sponsored Links
This is from a reply I gave another guy on another forum regarding the panting of MDF

I have complemented you on this advice before village and i have a follow up question. i have some mdf units to paint, will the above technique work on mdf? i am after a top notch finish, but do not want to spray but i am happy to use a roller and brush and do plenty of sanding...
November 5, 2008 | Tarquin


The long and short of it is yes.
The part of the project that will let the side down will be the cut edges of the MDF, this due to the exposed / cut edges of MDF is like sponge and will soak up paint like its going out of fashion.
Remember to paint the edges that wont be seen with the same care and attention

By going the extra mile on the edges you will stop the MDF acting like a sponge and it is the edges that will let the side down and be the first part to allow the ingress of water.

If you attempt to apply paint to the raw cut edge of MDF, regardless how good the saw cut or router cut is you will be painting for ever and a day and you will still be disappointed with the result. So you need to seal the raw edges. This is not complicated or expensive and doesn’t require spending your hard earn cash on fancy primers / sealers.
First method
Plane and sand all raw edges of the MDF to 180 grite, this not only make the edges flat and smooth but will partly / sort of seal the edges (close up the fibbers) not forgetting to remove the arris. Now you need to apply one - three coats of normal (bog standard) acrylic primer to the raw edges only, no need at this stage to paint the sides of the cabinet / panel, denibbing between coats with 180 grite (it doesn’t mater if you get paint on the face of the panels). In fear of having one of “oil-based undercoat” AKA Big Add empty paint cans thrown at me, I actual use emulsion paint if I haven’t got any acrylic primer. You should be able to get 3 coats on in the day.
Once you are happy with the cut edges you can now apply a coat of bog standard primmer all over the panel using a roller.
Now finish as above with proper oil based eggshell.
Second method
This method will cost you a few extra pennies; Once you have planed the edges of the MDF apply iron on edging (doesn’t mater about the colour as you going to paint it) sand the iron edging once applied again not forgetting to remove the arris. Prime the complete panel with that very expensive bog standard acrylic primer.
Now finish as above with proper oil based eggshell.
If you have laminated two of more pieces of MDF together say two 12mm to get 24mm then you can apply iron edging to these edges to cover up the glue joint. Iron on edging is available 50mm wide.
 
Awbcm thanks for your reply.

Do you know if the BIN primer is good enough - it says that its resin contecnt is 100 % shellac.

FOr the denibbing, is this to be done by hand or can i do it with the palm sander? Also, when should you stop sanding (i.e. will it be very smooth and obvious or should I wait for all the coats to have gone on before expecting a smooth finish?).

Also, do you think using aerosol primer/pain will give a smoother finish than roller after sanding?

Thanks a lot!!!
 
just denib by hand a light brush over with the paper you don't want to keep exposing raw MDF after every coat.
BIN seems a bit pricey just do as AWBCM says and use bog standard acrylic primer.
 
Word of warning on using spray paint; spray paint is very much unforgiving and will show up any in perfections, so if your preparation is some what lacking (crap) you will get rubbish looking finish. But if you will find a oil based paint is more forgiving.

Denib by hand

Bog standard acrylic primer is al you need


Below is the complete question and my first reply. You may find it of help.

We've just had some bespoke kitchen units built. They were delivered yesterday and are the wrong colour!!!!
It's actully our fault as we signed off on the schedule of works which have the incorrect colour for the units. I think it's going to take a little time to get them taken away and painted by the company that made them and will also cost a bit more and we have already shelled out a lot on the units.
I was thinking about painting them myself so wanted to find out the best paint to use and what preparation if any is required. They are wood and are currently a light cream colour and i will be painting them a darker colour.

Many thanks
November 5, 2008 | L Harris



You can paint the units, be a good idea to put a primer coat of something like zinsser 123 to act as a base for your new paint. Forget any water based finish applied by brush, it will look ropey and you`ll regret it. You could gloss or eggshell, but to be honest you`re going to have to be a good painter to get any sort of finish comparable to the factory.
I`d suggest finding someone that can spray them for you, you might persuade a car spraying workshop to do it for you which i think is the best option, you could hire someone or you could hire the gear and do it yourself. Dont forget to use an appropriate undercoat

November 5, 2008 | Darren

Oil based egg shell on my and it is very good. It gives a very deep low sheen finish of around 20% gloss.

I prep the timber as normal ( well normal for me ) sanding to 180 grit. Appling a knotting solution to all knots. Primmer / sealer coat and a minimum of two oil based undercoats denibbing between coats. Before applying the first coat of egg shell I de-nib the undercoat using 320 grit silicon carbide lubricated with white spirits not water, to remove all bush marks or roller marks. If you use water and you sand through to the timber or MDF or any other man made board water will raise the grain and give tremble problems with normal grade MDF. So it is safer to use white spirit as a lubricate, well in think so.

Apply the first coat of egg shell using a 100mm good quality foam roller, going across the grain or short ways and finishing with light storks with the grain or long ways. De-nib as above with 500grit and white spirit again to remove all roller marks. Thin the last and final coat of egg shell with turpentine not white spirit by about 5-10%. Again using 100mm foam roller as above. By using turpentine or turpentine substitute you should not notice the slight dulling of the gloss level but you would if you use white spirits. By thinning the final coat it will level itself a little flatter.
You can us turpentine or turpentine substitute as a lubrication but as turpentine or turpentine substitute is considerably more expensive than white spirit I use white sprit.
Basically by using the above method you should get close to a cabinet maker finish or coach painters finish.
And don’t forget to use a tack cloth to remove all the dust left by the busting brush.

To store your roller and stopping it from hardening put about half a egg cup of turpentine in a sealable plastic bag bigger, place the roller in the plastic bag expel the air seal and work the turpentine into the roller. When you want to reuse the roller, remove any excess turpentine using a clean rag and rolling out on a scrap board ( I tend to use an old sheet of plaster or cardboard it draws out the paint from the roller a lot faster )


To give you some idea of the cost of spraying a kitchen unit inside and out in precatalyst high density lacquer, I would charge £50 - £100 per unit. Door and drawer fronts only £25.00 each
 
If you can’t cut the mustered on the preparation and we all know preparation is king when it comes to get a first class finish, then you will get a rubbish finish.

Not even a blind man on a double decker bus on the way to Blackpool would be pleased to see it.

Its all in the preparation

Don forget that starts with the planning and the cutting of the material
 
Guys thanks again for your help.

OK here's what I'm doing ... see what you think ...

1. Sanded some bits down to 180 grit (the more visible ones), the less visible to 120.

2. Cleaned all bits with a damp cloth and left overnight to dry.

3. Taking awbcm's advice and not using spray paint. I did buy the (shellac based) Zensser BIN though but am applying it with a brush.

4. Will do 3 coats and rub down each coat with 320 grit paper (by hand and lightly!!! :D )

5. Will apply silver paint as finish.

On point, 5, should I also rub down with 320 in between coats if i do 2 top coats? Also, do i rub down the last coat?

Other than the above questin, is my prep ok or should i be doing smoething else?

Thanks again! ;)
 
1. Sanded some bits down to 180 grit (the more visible ones), the less visible to 120.

Sand down to 180grite (Higher the number the finer the grit)

2. Cleaned all bits with a damp cloth and left overnight to dry.

No remove dust with dusting brush and apply your first coat of bog standard acrylic primer



3. Taking awbcm's advice and not using spray paint. I did buy the (shellac based) Zensser BIN though but am applying it with a brush.

Return expensive primer and get refund.

5. Will apply silver paint as finish.

Denib between all coats
 
Awbcm

THanks again for your advice. I did go ahead and sand everything to 180.

However, i must admit that i kept (and used) the primer. The main reason is that I spent an hour crossing london to get it and frankly for £13.99 it wasn't worth doing the journey again just to return it. It is a strange primer. I'd previously used an acrylic primer by MacPhersons which is very thick. The Zensser one is incredibly runny. It goes on pretty easily and has a really nice finish when you sand it, it almost looks like sanded woodfiller (although I failed to get it this good on the face of the mdf (i.e. for some reason the sanded finish was amazing on the sawn/routed edges but not as good on the back/front of the mdf - maybe more sanding needed?).

Having said that, although the bits arent 100 percent glass smooth, I am happy with the results. I've not yet finished all the pieces though so will report back when I'm totally done. The results so far are way better than my previous shelves, etc. with the macphersons. But I must admit that a lot more prep and effort has gone into this project and like you rightly said, its all in the prep.

I was wondering whether preping, priming and sanding shelves, drawer fronts, etc will now yeild much more perfect results given that they are simpler shapes than the V- grooved triangles, etc. that i'm painting for this mirror.

SOrry for the long ramble, what i really wanted to say was thanks ( to you too Chappers)! :)
 
No problem lets see some photos when you have finished including close ups so we can see all your hard work in its glory.
 
stunning bit off work well done :D :D

only comments i would make is best to
make a few inches smaller as a margine around looks better
and would also allow more flexibility in the room
for example if your new bed has a slightly higher headboard or you wanted to place abouve a chest off drawers
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top